Revox A77 difference in volume when playback

[Gast]

Hi, i recently obtained a Revox A77 Mk IV.
When having a listen to it I found out that there is a large difference in the volume. The left channel seems to produce less sound then the right channel. When turning the balance button you can more or less solve the problem but you still hear the difference between the left and right channel.

The heads are in good order. The are very clean and the rollers are also in good condition.

I changed the playback amplifiers from possition on the switchboard and the problem moved as well. So I guess that one board is not working correctly.
What can I do with this? Do I have to replace the transistors on the board or can this problem be solved in another way?

Or do I have to look elsewhere? Is there another way to solve this problem?

I'm also looking for the amplifier board. Does anyone have a pair for me?
We can talk about the price.

I recently started with revox (the A77 is my first one).

Many thanks for your advice.

Steve
Belgium

[heinz]

AW: Revox A77 difference in volume when playback

Hello Steve,
first of all, you should take a close look at the trim potentiometer (20 kiloOhm)
and replace both of them if the colour of the metal parts has turned to black.
But keep in mind that after replacing the potentiometers you must calibrate the reproduce amplifiers.
I do not think that transistors will have to be replaced, but the electrolytic condensers may cause trouble, especially the white ship-shaped one.
With kind regards,
Heinz

[4579456]

Re: Revox A77 difference in volume when playback

I had closer look to the potentiometers and they still have contact with the metal. They look fine to me and a measurement was fine.

thanks to another revox fan I obtained a set of push-in panels for the A77 and replaced mine with the new ones.

result: I still have a difference in the volume.

When starting the tape I noticed somthing: when playing I noticed a drop back of the volume on the left side too. And then it suddenly comes back.
When the sound drops back the difference with the right channel is still there.

when posting my question I saw I made a mistake: the left channel is ok, but the right channel isn't. I have to turn the balance completely on "right" to get a better sound. There is still some sound on the right channel but the difference with the left one is enormous.

So the push in panels can be excluded, the heads are fine, the tapes has the wright bias (its a BASF LPR35), the switchboard can also be expluded because I completely replaced it with a spare one. What else could it be?

[4579456]

AW: Revox A77 difference in volume when playback

I did have a test this afternoon. I connected my A77 to my hifi set and I recorded some music that came from a cd. The tape I used is a brandnew lpr35 from RMGI. The type of tape: NAB.
The balance button was set on Input and the record level buttons were set at 3 (all 2 of them)

When I played the tape I noticed that my problem with the difference in the volume level is also present in the recording. So my playback amplifiers are not broken. And for those thinking something is wrong with my headset: it's in perfect order. When I called up a friend who also has a A77 but in perfect condition I went at his place with my freshly made tape. At his A77 the tape played fine with no difference in volume.

So I have a very nice piece, an A77 but with a difference in volume. What can I do about it? The amplifier cards are ok, the recordinghead is ok, the playback head is ok, the oscilator card has been replaced, fully cleanded but what is the problem with the machine?

My last goal is to replace the potentiometer used for the Balance. If this doesn't help I will throw away the machine.
Grrrrrrrrrr

Steve

[4579456]

AW: Revox A77 difference in volume when playback

Eureka

I've got it!

It seems the balance button is defective.

I got the balance button out and rewired the whole thing so I don't need a balance potentiometer and it works ! My A77 is up and running but without a balancebutton. So I'll just have to find a new or used one.

When I choose stereo I get stereo, when I choose mono I and II I get mono and that's just fine.

steve

[4579456]

AW: Revox A77 difference in volume when playback

hello revoxfans

My A77 is now in full working order!

I obtained a new potentiometer for my A77 thanks to another revox fan from Belgium. So my problem with the difference in volume is solved.

What I did this afternoon: I cleaned the erase head with some alcohol and yes indeed some dirt did come of but not much. I also cleaned the recording head and the playbackhead. So everything is shinning as new.

I made a recording of a cd to have a listen if the soundquality is ok and I must say it's outstanding! (I used a brand new tape of RMGI, a LPR35).

What I still need to do: some cleaning and I'll probably have to measure my A77 out to see if he (or she) needs some adjustment.

So for the moment I'm in 7th heaven!

The recording I made: I want You by Marvin Gaye and I must say it sounds even better on tape.

bye for now

Steve